The Hangover Part II

The Hangover Part III star, 34, is engaged to personal trainer Lia Smith, PEOPLE has confirmed.

"They're very happy," a source says of the pair, who was first publicly linked this past New Year's Day when they were photographed in Smith's native state Hawaii, where they were "very cute" and affectionate, according to an onlooker at the time.

The biggest comedy of the summer season includes a few familiar faces – and one you might not know is so familiar. Here are five things you might not know about Crystal, the scene-stealing monkey of Hangover 2:

1. In real life, she doesn't smoke.Director Todd Phillips jokingly said that after training Crystal to play a chain-smoking drug mule, he had "PETA after me because the monkey's become addicted to cigarettes." Phillips later had to clarify that he had been joking. Crystal's trainer, Thomas Gunderson, worked with his 17-year-old monkey so that she could hold a hollow prop that looked like a cigarette (the smoke effects were added later through CGI). She also learned how to use several different kinds of lighters (that didn't have real flames).

Ken Jeong donned his birthday suit in The Hangover and he does it again in The Hangover Part II. But before he displayed his body, he asked for approval from one person – his wife.

"I got her permission. I'm not stupid," the actor, who plays flamboyant, foul-mouthed gangster Leslie Chow, told PEOPLE at the film's Los Angeles premiere this week. "I ran it by her before I ran it by [director] Todd Phillips."

And obviously his wife, Tran, gave her hubby the green light. "I'm very blessed to have a supportive wife," said Jeong. "In fact, she said this will be a feel-good movie because every guy will go home feeling good about themselves."